1/*
2 * Copyright 2012-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#pragma once
18
19#include <stddef.h>
20#include <stdint.h>
21
22namespace folly {
23
24template <typename T>
25class GroupVarint;
26
27namespace detail {
28
29template <typename T>
30struct GroupVarintTraits;
31
32template <>
33struct GroupVarintTraits<uint32_t> {
34 enum : uint32_t {
35 kGroupSize = 4,
36 kHeaderSize = 1,
37 };
38};
39
40template <>
41struct GroupVarintTraits<uint64_t> {
42 enum : uint32_t {
43 kGroupSize = 5,
44 kHeaderSize = 2,
45 };
46};
47
48template <typename T>
49class GroupVarintBase {
50 protected:
51 typedef GroupVarintTraits<T> Traits;
52 enum : uint32_t { kHeaderSize = Traits::kHeaderSize };
53
54 public:
55 typedef T type;
56
57 /**
58 * Number of integers encoded / decoded in one pass.
59 */
60 enum : uint32_t { kGroupSize = Traits::kGroupSize };
61
62 /**
63 * Maximum encoded size.
64 */
65 enum : uint32_t { kMaxSize = kHeaderSize + sizeof(type) * kGroupSize };
66
67 /**
68 * Maximum size for n values.
69 */
70 static size_t maxSize(size_t n) {
71 // Full groups
72 size_t total = (n / kGroupSize) * kFullGroupSize;
73 // Incomplete last group, if any
74 n %= kGroupSize;
75 if (n) {
76 total += kHeaderSize + n * sizeof(type);
77 }
78 return total;
79 }
80
81 /**
82 * Size of n values starting at p.
83 */
84 static size_t totalSize(const T* p, size_t n) {
85 size_t size = 0;
86 for (; n >= kGroupSize; n -= kGroupSize, p += kGroupSize) {
87 size += Derived::size(p);
88 }
89 if (n) {
90 size += Derived::partialSize(p, n);
91 }
92 return size;
93 }
94
95 private:
96 typedef GroupVarint<T> Derived;
97 enum { kFullGroupSize = kHeaderSize + kGroupSize * sizeof(type) };
98};
99
100} // namespace detail
101} // namespace folly
102